Thickened, water-based, process fluids which exhibit shear-thinning behaviour are useful in a number of technical fields.
In particular for hydrocarbon well applications such fluids are used as e.g. drilling fluids, water control fluids and fracturing fluids. A typical rheological requirement for the fluids is a reversible and severe drop in viscosity when the shear rate imposed on the fluid is increased.
Aqueous drilling fluids commonly contain clay particles and thickening agents. For example U.S. Pat. No. 49,990,268 discloses a drilling fluid which contains negatively charged bentonite particles and positively charged mixed metal hydroxide particles and which is thickened by a heteroflocculation mechanism involving the formation of a gel network based on Coulombic (electrostatic) attraction between the bentonite and mixed metal hydroxide particles. A commercially available calcined mixed metal hydroxide powder thickening agent supplied by M-I L.L.C. is sold under the name Visplex™.
Clay-free drilling fluids containing viscosifying aluminium hydroxide compounds are also known, as disclosed e.g. in U.S. Pat. Nos. 4,240,915, 4,389,319, 4,349,443 and 4,486,318.
However, the stability of the rheological behaviour of these fluids may be threatened by e.g. degradation at elevated temperatures, oxidation and/or the presence of contaminating salts, and an object of the present invention is to provide a water-based process fluid which exhibits acceptable rheological behaviour over a wide range of operating conditions.